Tubular apparatus for the continuous completion of hydrocarbon wells, and corresponding laying method

ABSTRACT

Described herein is a tubular apparatus for the continuous completion of wells for hydrocarbons, of the type comprising a flexible cylindrical wall ( 11; 11 ′) defining inside it a hollow passage ( 19 ) suitable for being wound, in particular on a spool, and laid for use in the step of completion of a drilling well. According to the invention, said cylindrical wall ( 11; 11 ′) comprises a fabric ( 12, 13, 15; 12′, 13′, 15 ′) including inside it at least one gap ( 14; 14 ′), which develops in the axial direction of said cylindrical wall ( 11 ), said fabric ( 12, 13, 15; 12′, 13′, 15 ′) comprising means suitable for operating under traction ( 15; 15 ′) when within said at least one gap ( 14; 14 ′) a pressurized fluid ( 20 ) is present injected for stiffening the tubular apparatus ( 10; 10 ′).

The present invention relates to a tubular apparatus for the continuous completion of wells for hydrocarbons of the type comprising a flexible cylindrical wall defining inside it a hollow passage, suitable for being wound, in particular on a spool, and laid for use in the step of completion of the drilling well.

The tubing systems used in the completion of wells for hydrocarbons usually consist of tubular steel elements made in discrete sections, for example, with a length of nine metres, connected together via male-female threaded joints.

Tubing of this sort implies the presence of operators who carry out the operations of cleaning of the joints and checking of the integrity of the threads, fit, greasing, controlled tightening, and fluid tightness of the joint. Moreover, the presence of the lubricant in the joint prevents the use of the tubing as a conductor for carrying electric power and/or data.

It is known to use, in non-permanent applications, flexible tubing for conveying hydrocarbons which are made of steel-reinforced polymeric material, which are resistant to hydrocarbons, CO₂, and H₂S, and withstand pressures of the order of hundreds and thousands of bar.

For instance, the document No. GB2287270A describes a system consisting of a flexible metal tube, for example a spoolable tube, used as coiled tubing. Integrated already, in the stage of production, in said tubing, which has a flexibility such as to enable winding thereof on a spool and transport thereof in situ, are all the mechanical components normally used in the process of completion.

This type of solution, which is based upon a flexible tube, presents the advantage of enabling continuous laying, in particular lowering and unwinding of the tube without any interruption; however, it is not suited to being installed permanently in the well on account of the mechanical stresses to ‘Which it would be subjected, for example, variations in pressure or stresses involved in supporting the equipment for the well completion, such as for example valves, or packers, or the weight of the tube itself.

The object of the present invention is to provide a flexible tubular apparatus suited for being wound, in particular on a spool, and continuously laid for completion of the well, which can provide permanent installation.

According to the present invention, said object is achieved thanks to a tubular apparatus, as well as to a corresponding laying method, having the characteristics recalled specifically in the annexed claims.

The invention will be described with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:

FIG. 1 is a principle diagram of a first embodiment of the tubular apparatus according to the invention in a first configuration of use,

FIG. 2 is a schematic cross-sectional view of a detail of the tubular apparatus of FIG. 1;

FIG. 3 is a principle diagram of the tubular apparatus of FIG. 1 in a second configuration of use;

FIG. 4 is a schematic cross-sectional view of the detail of the tubular apparatus of FIG. 1 in a second configuration of use;

FIG. 5 is a schematic cross-sectional view of a second embodiment of the tubular apparatus according to the invention;

FIG. 6 is a principle diagram of a first method for laying the tubular apparatus according to the invention;

FIG. 7 is a principle diagram of a second method for laying the tubular apparatus according to the invention; and

FIG. 8 is a principle diagram of a third method for laying the tubular apparatus according to the invention.

In brief, a tubular apparatus is proposed that can be laid as a flexible object, via a specific configuration of the walls of the tubular apparatus. Said specific configuration envisages that the tubular apparatus, made via a tube with cylindrical wall made of fabric or interwoven fibres, identifies, within the wall, at least one gap in the axial direction of the tube. The gap comprises means for operating under traction in the structure of the wall when present within the gap is a pressurized fluid, i.e., a fluid such as to determine a resultant pressure from inside the gap outwards, injected for stiffening said tubular apparatus. In particular, the cylindrical wall defines, via the respective interwoven fibres, a three-dimensional structure, or three-dimensional fabric, comprising an outer wall, an inner wall, one or more gaps comprised between said outer and inner walls, and the means suitable for operating under traction.

By “three-dimensional structure” or “three-dimensional fabric” is meant in general a fabric comprising a first surface defined by the interwoven fibres and a second surface defined by the interwoven fibres, said first and second surfaces being set at a distance from one another such as to define a volume of space between them. Said space comprises interwoven fibres for defining one or more gaps, with a development principally in the axial direction of the tubular apparatus, and means suitable for operating under traction, in the form, for example, of threads or yarn or layers of fabric, arranged in said space for interconnecting the first and second surfaces. That is, the threads or yarn or layers of fabric extend continuously from the interwoven fibres of one surface to the interwoven fibres of the other surface. Hence, the threads or yarn or layers of fabric that traverse the gap and operate as means suitable for operating under traction are fibres that belong to the weave of both of said surfaces.

Represented in perspective in FIG. 1 is a tubular apparatus 10 according to the invention. Just one short segment of said tubular apparatus 10 is represented in FIG. 1, but in general said apparatus comprises a tube in the form of a closed hollow solid, which, in a resting condition, i.e., when it is not, for example, bent or squeezed, or, as explained in detail in what follows, when a fluid is injected therein, has a cross section that is preferably constant in shape and area and extends for a length at least ten or one hundred times greater than its internal diameter. Said tubular apparatus 10 comprises a wall 11, substantially having the form of a wall of a cylinder and thus defining inside it a hollow passage 19, designed, for example, to allow passage of a flow, for instance, a flow of a liquid hydrocarbon, in the axial direction of the tubular apparatus 10. Said wall 11 is flexible, made of a three-dimensional fabric of fibres that delimit at least one gap 14, which substantially also has the shape of a cylinder or cylindrical annulus developing in the axial direction of the tubular apparatus 10.

A structure of this type can, for example, be obtained according to what is illustrated in the cross sections of FIGS. 2 and 4. FIGS. 2 and 4 show cross sections of the tubular apparatus 10, i.e., sections perpendicular to the longitudinal axis of said tubular apparatus 10. The portions of cross section of wall 11 of FIGS. 2 and 4 are in actual fact arcs of circumference, but are here represented straightened for simplicity, given the difference of dimensions between the overall diameter of the tubular apparatus 10 and the width of the gap 14, as described more fully in what follows.

Illustrated in FIG. 2 is a cross section of the wall 11, where there may be noted interconnection fibres 15 that join an inner wall 12 and an outer wall 13, passing through the gap 14. Also said interconnection fibres 15, as may be inferred from FIG. 2 and as is explained in detail hereinafter, are continuous fibres of the three-dimensional fabric; they are fibres belonging to the weave of the walls 12 and 13. The inner wall 12 faces inwards, i.e., it delimits the hollow passage 19 of the tubular apparatus 10 where the flow to be conveyed passes, whereas the outer wall 13 faces outwards, for example, towards the well walls in which the tubular apparatus 10 is inserted. The wall 11 of the tubular apparatus 10 is obtained via a fabric of fibres, the weave of which develops in three dimensions. Illustrated in particular in FIG. 2 is a double interconnected layer, in which two parallel fibres identified by the respective warp threads 12 a and 13 a (or, respectively, weft threads) of the wails 12 and 13 form as many parallel layers of fabric set at a distance apart from one another, to delimit the gap 14. It is envisaged to use for the wall 11 fibres with high mechanical performance under traction, for example, aramide fibres or carbon fibres. The interconnection fibres 15 correspond to some well fibres 12 b and 13 b (or, respectively, warp fibres) of the parallel fabrics that constitute each layer or wall 12 and 13, which fibres intersect, constraining together the structures of the layers, i.e., the structures of the two walls 12 and 13. This consequently produces a three-dimensional fabric in which all the fibres work under traction with respect to injection of a fluid in the gap 14, for example, with respect to forces that tend to press the walls 12 and 13 apart and result from the pressure of the fluid, as will be explained in greater detail in what follows. This enables injection in the gap 14 of fluids at very high pressures with optimal distribution of the loads on the structure.

Three-dimensional fabric structures of the type illustrated in FIG. 2 or FIG. 4 are produced, for example, by the company Pascha Velvet BVBA.

It is envisaged to impregnate the fibre of the inner wall 12 and the outer wall 13 with an impermeabilizing agent, in particular with a polymer, to obtain coatings 16 that guarantee fluid tightness for the fluids conveyed in the passage 19. For this purpose, fluorinated polymers may, for example, be used, which guarantee excellent chemical resistance to hydrocarbons, H₂S, and CO₂.

The process of impregnation may, for example, be a process of impregnation, at high temperature, of the fabric of fibres with the polymer similar to the one used for the production of the rubber composites reinforced with polyester fabric used in the production of membranes for pneumatic valves.

More in general, the tubular apparatus 10 for example comprises, as illustrated with reference to FIGS. 2 and 4, walls 12 and 13 obtained through a

respective single layer of three-dimensional fabric, i.e., a layer of weft and warp threads, for instance, the surfaces of which facing the inside and the outside of the tubular apparatus 10 are rendered impermeable via surface treatments. The impermeabilization may be obtained also using one of the following treatments of the surfaces of the single layer:

-   -   via deposition of an impermeable polymeric film (silicone, PTFE,         or other fluorinated polymers) by means of plasma or thermal         spraying;     -   via spray coating of polymeric paints;     -   by means of deposition by fusion of an impermeable polymeric         film on the outer wail of the tubular apparatus 10, which         enables coating of the entire surface of fabric that comes into         contact with the external and internal environment of said         tubular apparatus 10;     -   by means of kiss-coating, slot-die, or other processes of         roll-to-roll spreading of the surfaces of fabric in contact with         the external and internal environments of the tubular apparatus         10 with fluorinated polymers (for example, Teflon®, Zonyl®).

It should be noted that in this way it is sufficient to treat the surface of the three-dimensional fabric, as compared, instead, to tubing of the prior art (not made of metal), which envisaged impermeabilization by gluing or superposition of one or more layers of impermeable material.

It is provided that, during laying or when the laying operation is completed, the gap 14 is filled with a pressurized fluid 20, at a pressure preferably higher than the pressure on the outside of the tubular apparatus 10 in the position of laying, as illustrated in FIGS. 2 and 4, which show the tubular apparatus 10 in perspective view and the wall 11 in cross-sectional view. The tubular apparatus 10 behaves like a rigid object by virtue of the pressure of the fluid 20 injected.

The fluid may in general be a pressurized fluid, such as for example water, designed to give stiffness to the apparatus via pressurized injection.

However, according to a further aspect of the invention, the fluid 20 injected into the gap 14 may be a cement or a resin or some other material capable of solidifying; in this case, the tubular apparatus 10, once solidification has occurred, will to all effects be a rigid object made of composite material.

As regards the pressure values, in general for inflating a collapsed tubular element immersed in a fluid, which is a structure to which the tubular apparatus 10 can be likened when the fluid flows in the passage 19, at a pressure P, it is necessary to exert a pressure of inflation, or injection, P+ΔP, where ΔP is an overpressure necessary to compensate for the head losses within the tubular element. The tubular apparatus 10 is configured for being inflated by means of injection of a fluid into the gap between the walls of the fabric. Moreover, the tubular apparatus 10 is configured for being installed also in extraction wells, where the pressures of the fluid to be extracted are indicatively comprised between 10² bar and 10³ bar.

In general, in a system such as the tubular apparatus 10, the overpressure ΔP depends upon the viscosity of the injected fluid, upon the characteristics of the injection channel, i.e., upon the characteristics of the gap 14, and upon the length of the path that the injected fluid has to traverse.

Since the fibres of the three-dimensional fabric of the tubular apparatus 10 present a high tensile strength, they enable injection into the gap 14 of a viscous fluid, for example, an epoxy resin, the viscosity of which is comprised, for instance, in a range of between 100 and 500 mPa·s, with an overpressure ΔP to compensate for the head losses that can reach up to 10-100 bar.

An epoxy resin with viscosity of 250 mPa·s may, for example, be injected, exerting a maximum overpressure of 100-200 bar for every 100 m of injection path, i,e., with a length of the tubular apparatus 10 depending upon the rheological characteristics of the fluid and the desired rate of injection.

Consequently, the tubular apparatus 10 is configured, via the cylindrical wall made of fabric that defines, via the respective interwoven fibres, a three-dimensional structure, and via the means suitable for operating under traction comprised in said structure, for withstanding a stress on the walls of the three-dimensional fabric, when a fluid injected under pressure for stiffening the tubular apparatus is present within the gap, with an overpressure ΔP that is, for example, higher than 10 bar. For instance, said overpressure ≢P that can be sustained may even be higher than 100 bar. Again for example, said overpressure ΔP that can be sustained may even be higher than 1000 bar.

Said overpressure ΔP that can be sustained by the apparatus 10 is preferably comprised between 100 and 200 bar.

It should be noted that the larger the number of interconnection threads between the walls, the greater the maximum overpressure that can be exerted in the gap; consequently, the tubular apparatus can be sized for withstanding higher pressures by working on said parameter.

The structure of the wall 11 may in general comprise a number n of layers of fabric that delimit n-1 concentric gaps 14, where n is an integer greater than or equal to one. In general, this can be obtained via the arrangement of a number of complete concentric walls 11 or via a wall having an outer wall, an inner wall, and a plurality of separating walls for identifying the various concentric gaps.

The structure of the wall 11 can be made with topologies of structure of the fabric that may even differ from the one illustrated by way of example in the present description but in which in any case the criss-crossing of the layers of fibres delimits one or more gaps in which the filler fluid 20 can be injected, for example, topologies of fabric with honeycombed cross section.

Illustrated in this connection in FIG. 5 is a variant embodiment of the tubular apparatus 10, designated by 10′, in which a wall 11′ delimits between its inner wall 12′ and its outer wall 13′, which are coated with impermeabilizing polymeric layers 16′, a honeycomb structure of gaps 14′ corresponding to the cells of the structure. The wall 11′ is illustrated in cross-sectional view; consequently, also the gaps 14′ develop in the axial direction of the tubular apparatus 10′. Separating walls 15′ of the cells that determine the plurality of gaps 14′ operate in this case at least in part as means operating under traction in regard to injection of a fluid into the gaps 14′.

The layers of fibres that delimit the gaps 14, including the inner wall 12 and the outer wall 13, as has been said, may present, on one or both of the faces, a coating of polymeric material. Said coating may be specialized for performing various functions, amongst which:

-   -   being impermeable to various substances, amongst which water,         CO₂, H₂S, hydrocarbons, as well as to the components of the         fluids 20 injected, while being soluble to some substances;     -   allowing selective passage of certain substances;     -   degrading at a set temperature or in set conditions; and     -   allowing passage of the fluids once a given pressure         differential has been exceeded.

The tubular apparatus 10 may be used in multilayer structures comprising layers of other materials that perform specific functions, for example, layers of fire-proofing or self-extinguishing material.

It is possible to exploit to advantage the characteristic of the tube according to the invention of enabling continuous laying or in any case laying in stretches of hundreds of metres or kilometres and consequently with a very small number of joints, for integrating therein in a simple way systems for the transmission of energy and data, in addition to sensor systems.

The structure of the wall 11 can integrate cables for conveying electric power, laser beams, or signals for carrying data, for example, metal or optical-fibre cables.

The structure of the wall 11 can integrate sensors and sensor systems for checking the operating conditions of the tube; they may, for example, be sensors for detecting mechanical stress, deformation, failure, deterioration of the polymeric coating, pressure, temperature, etc.

The structure of the wall 11 may integrate sensors for analysis of the fluid conveyed, such as for example pressure sensors, temperature sensors, sensors for chemical composition, multi-phase flowmeters, sensors for detecting electrical properties, etc.

The laying method contemplates that the gap 14 is initially empty; consequently, the tubular apparatus 10, which can be a continuous tube of the length desired and allowed by the properties of the fibre used, and hence even several hundreds of metres or kilometres, is flexible and can thus be wound on a spool, carried to the site where it is to be laid, unwound, lowered, and positioned in a continuous way employing very simple laying processes.

As illustrated with reference to FIG. 6, the laying method may, for example, be carried out applying a weight 30 at the free end of the tubular apparatus 10 on the spool and lowered by gravity within a well 100. Said first embodiment of the laying method is defined in the sequel of the description as “simple laying”. With this simple-laying method, the tubular apparatus 10 is stiffened once the laying operation is completed by injecting a fluid 20 into the gap 14.

The laying method may, for example, also be carried out as illustrated with reference to FIG. 7, applying, at the free end of the tubular apparatus 10 wound on a spool, a so-called liner, or guide tube 32, and lowering in parallel, for example, applying thereto a weight and possibly using a winch 34 set at the bottom of the well for pulling the liner 32 working on the two pipes from a head 36 of the well 30. Said second embodiment of laying method is defined as “parallel laying”. Using this laying method the tubular apparatus 10 can be stiffened during laying by injecting a fluid 20 into the gap 14, to allow, for example, inspection of the integrity of the tubular apparatus 10 during its descent into the well.

The laying method may also be carried out, for example, as illustrated with reference to FIG. 8, by folding the free end of the spooled tubular apparatus 10 outwards and securing it with an appropriate support in the point of start of laying, for instance, at the head of the well 36. An annular carriage 21 is inserted as positioning device in a folded-back portion 27 thus obtained to facilitate descent of the tubular apparatus 10 under its own weight, to prevent the radius of curvature of the folded-back portion 27 from dropping below the threshold value of damage to the wall 11 and to contribute to isolation of the two separate stretches of gap of the folded-back portion 27. The tubular apparatus 10 is thus lowered, exploiting in an alternative or combined way the effect of the weight of the carriage 21, the injection of pressurized fluid 20 from the constrained end of the tubular apparatus 10, and, in the example of FIG. 8, a further drawing mechanism 25, fixed with respect to a drilling string 40 in the proximity of the drilling bit 42. In this case, the drawing mechanism 25, substantially a pair of arms that extend radially from the string with end wheels for engaging in the plane of the carriage 21 set vertically, operates in such a way as to exert a downward thrust. This third embodiment of the laying process is defined as “folded-back laying”.

The tubular apparatus 10 according to the invention can be used for various applications in the sector of extraction of hydrocarbons, for example, for obtaining production tubing for conveying from the area of production to the head of the well, for “workover systems”, namely, systems for repairing damaged tubing, for casing, i.e., the reinforcement that isolates the well and prevents collapse thereof, and for systems of coiled tubing and liners for operations in the well or for conveying process fluids.

A first application may include the use of the tubular apparatus 10 for obtaining of a production tubing. In this application, preferably the tubular apparatus 10, in the absence of fluid 20 in the gap 14, given that it is flexible, is squeezed until it assumes the form of a ribbon to enable it to be carried more easily wound on a spool to the laying site.

The tubular apparatus 10 for application as tubing is preferably lowered into the drilling wells according to the simple-laying method or the parallel-laying method, as described previously. The weight 30 used in simple laying may in this case be the packer used for isolating the tubing from the area of production of the well. Once the packer has been blocked at the bottom of the well, the tubular apparatus 10 is set under traction, and then the fluid 20 starts to be injected into the gap 14.

An important advantage of the parallel-laying method, as has been mentioned, is represented by the possibility of inspecting, visually or with non-destructive testing systems, the integrity of the tubular apparatus 10 during its descent into the well.

In this application, the fluid 20 may, for example, be a bicomponent resin, selected in such a way that its hardening time is much longer than the time necessary for laying the system of tubing or a heat-hardening resin that is activated when the laying operation is completed, for example, by blowing a jet of hot gas into the tubing.

According to a further aspect of the invention, the tubular apparatus 10, in particular for its application as tubing, may comprise two concentric gaps, separated by an impermeable wall of fabric in which a resin and its hardener are injected separately. The separating wall is functionalized in such a way as to enable interchange of the fluids when a set pressure or a set temperature is exceeded or again because the impermeabilizing layer is soluble for one of the two fluids.

As regards the amount of resin and rate of injection, by way of example, considering a tubing with a space of the passage 19 having an internal diameter of 3½″ (8.89 cm) and thickness of the wall 11 of 14 mm, the volume of resin to be injected is approximately 1.5 m³/km. Considering a rate of advance of the liquid of 0.5 m/s so as to guarantee a good wetting of the fibres and low head losses, a flow rate of 0.4 l/s is obtained, which can be obtained easily with piston pumps for high pressures normally used in the oil & gas sector. In said condition, a kilometre of tubing 10 is filled in approximately 35 min.

For said application of production tubing, there are, for example, used an outer wall 13 having a thickness of 2 mm, an inner wail 12 having a thickness of 2 mm, and a gap of 10 mm.

By way of example, for production tubing, low-viscosity epoxy resin and amine hardener may be used, which have excellent mechanical strength and resistance to heat, and chemical resistance to hydrocarbons and H₂S. The characteristics of said resin comprise: resin viscosity at 25° C. 800-1000 cps; hardener viscosity at 25° C. 180-300 cps; resin density (without fillers) 0.92-0.94 g/cm³; hardener density 0.94-0.96 g/cm³; resin/hardener weight ratio 2/1; gellying time at 25° C. 180-220 min.

Application of the tubular apparatus 10 in production tubing enables reduction of completion times, a lower thermal expansion, a weight up to three times lower than that of a traditional tubing.

In the application of the tubular apparatus 10 as production tubing, it is possible to include in the wall 11 of the tubular apparatus 10 cables for the transmission of electric power and/or laser beams and/or optical and/or electrical signals.

In a second application, it is envisaged to use the tubular apparatus 10 as workover system for the repair of damaged pipes.

For said application, for example, a stretch of tubular apparatus 10 of the length of some metres is located at a leak, for example, through the process of simple laying or of folded-back laying and is stiffened by injecting a fluid 20 into the gap 14.

The tightness of the workover system is guaranteed, for example, by the fact that the pressure of the fluid 20 injected into the gap 14, which is higher than the pressure inside the conduit to be repaired, pushes the outer wall 13 to adapt to the inner surface of the conduit to be repaired, and the polymeric coating 16 of the wall 13 thus performs the function of gasket.

An alternative embodiment of the tubular apparatus 10 as workover system envisages use of the tube where the wall 11 envisages two concentric gaps separated by an impermeable wall of fabric. The outermost gap contains a fluid, for example, a bicomponent epoxy resin, suited to repair the leak, the fluid 20 is injected into the innermost gap. The outer wall 13 is functionalized to allow passage of the fluid contained in the outermost gap when a pressure differential that is set up is exceeded. The tube is then located at the leak, and the fluid 20 is injected into the innermost gap at a pressure such as to involve outlet of the repair fluid in the proximity of the leak.

In a third application, it is envisaged to use the tubular apparatus 10 as casing.

For said application, the tubular apparatus 10 is laid with the folded-back laying method constraining the end of the tubular apparatus 10, for example, to the head of the well. The annular carriage 21 inserted in the folded-back portion 27 to facilitate descent of the tubular apparatus 10 can be pushed by the drawing device 25 fixed with respect to the drilling string 40 in the proximity of the drilling bit 42. While drilling is in progress, the combined action of the positioning device 21 and the drawing device 25 enables the folded-back portion 27 to advance downwards, following the hole of the well 100 In this step, the tubular apparatus 10 for casings is flexible and is not subject to marked friction in so far as the relatively moving surfaces are the facing ones in the folded-back portion 27, which can be easily lubricated with the same lubricating compounds contained in the drilling slurry.

In an application of the tubular apparatus 10 as casing, applied to the positioning mechanism 21, for example via a metal chain, is a flexible filling tube with which the fluid that will go to fill the gap 14 is conveyed, once the tubular apparatus 10 that provides the casing is set in position.

At the top of said filling tube, an injection tool is installed that has the task of perforating the inner wall of the tubular apparatus 10 and injecting the filler into the gap 14.

At the moment when drilling stops, for example, to add another length of drill rods, the injection tool perforates the inner wall 12 of the tubular apparatus 10 and fills the section comprised between the previous injection operation and the folded-back portion 27 with the filler fluid 20.

By appropriately adjusting the consolidation times of the fluid 20, stiffening of the tube may be obtained in a time shorter than that of addition of the new sections of drill rod.

At this point, drilling can proceed for the next section.

If need be, the injection tool for filling the gap 14 could perforate both of the walls of the tubular apparatus 10 for injecting material between the tubular apparatus 10 and the walls of the well, in order to consolidate them.

In a further application of the tubular apparatus 10 as casing, the fluid 20 may be injected into the gap 14 at the end of the tubular apparatus 10 constrained to the head of the well 36.

Laying may exploit the flexibility of the empty casing, continuously, and following the drill, i.e., the drilling head, at a distance of a few metres.

The application of the tubular apparatus 10 as casing enables a reduction of the drilling times, since drilling is of constant diameter, as well as a reduction of the times for completion mainly because it enables reinforcement of the well during stoppage for the addition of a drilling length to the drill rods. Moreover the safety increases in so far as it provides the possibility of following the drilling head from a distance of a few metres.

By way of example, the method may envisage lowering for stretches of constant diameter throughout the depth of the well, equal, for example, to 9⅝″ (24.4 cm). A 4000-m well may be completed in four steps:

-   -   laying of 500 m of 9⅝″ steel casing;     -   laying of 500 m of tubular apparatus 10;     -   laying of 1000 m of tubular apparatus 10; and     -   laying of 2000 m of tubular apparatus 10.

The drilling operations must be interrupted just four times for lowering the well completion. During drilling, the casing is stiffened in stretches of 27 m of length during addition of the drill rods.

In a further variant of the method, the tubular apparatus 10 can be produced in real time with a double carousel for weaving and two corona discharge devices for impregnation at high temperature.

To guarantee continuity of production without interfering with the drilling, the apparatuses must be positioned underneath the drilling plane, for example, in the drilling pool.

According to a variant, the initial and final sections of the stretches of tube 10 can expand more to be able to adhere to the joining areas of the previous and subsequent stretches,

Hence, on the basis of what has been described so far, the solution according to the invention, as well as its advantages, emerges clearly.

The tubular apparatus according to the invention advantageously comprises a three-dimensional fabric, without any interruption or seams that might alter homogeneity thereof, which identifies two weft-thread and warp-thread walls connected together via filaments that belong to weft and warp themselves of the walls. Since the interconnections between the two walls, i.e., the means for operating under traction, consist of filaments belonging to the walls themselves, they enable, following upon application of a local or extensive stress, such as, for instance, the pressure of an injection fluid, a homogeneous distribution of the stresses that affects the entire volume of the fibres of the fabric, not only the area in direct contact with the point or area of application of the stress. Said particular structure of the three-dimensional fabric enables very high stresses to be withstood since their intensity is distributed over a wider area than the one affected directly by the stress, making not only the fibres of the wall on which the force acts to work, but distributing the force over the interconnections, which in turn distribute it over the opposite wall. Without being tied down to any specific theory in this connection, the foregoing can be interpreted as a manifestation of how the stresses are not concentrated in a small area of the tubular apparatus or of its wails, but rather the stress vector is decomposed into infinitesimal stress vectors that act on the infinitesimal surfaces into which the fabric may conceptually be divided.

The use of said three-dimensional fabric, with the structure and configuration referred to above moreover advantageously makes available a fabric provided with a gap between the two walls, the weft-thread wall and the warp-thread wall. Within the gap, as has been mentioned, there can be injected a fluid at very high pressure, even of the order of hundreds or thousands of bar. The fibres of the fabric, following upon injection of the injection fluid, are stressed substantially along their axis, since they are, for example, weft-thread fibres in common between parallel layers of warp fibres. Stressed in this way, said fibres present mechanical properties of very high tensile strength and are able to withstand the tensile stress that is exerted from the inside towards the outside of the gap, also thanks to the aforementioned distribution of this stress over the entire surface of the fibres.

Furthermore, advantageously the tubular apparatus according to the invention uses a three-dimensional fabric of fibres, such as for example aramide fibres, characterized by very high values of tensile strength (in the case of aramide fibres, for example, up to three times the tensile strength of steel).

The tubular apparatus according to the invention is particularly advantageous in operations of spoolable tubing, as compared, for example, to a tubing made of metal material, in so far as it can he wound and produced industrially in the lengths required: since it is a continuous tubular, no joints are necessary, and this enables integration within the gap of metal wires or optical fibres for conveying signals and/or power, to be lowered, for example, continuously in extraction wells that are even several kilometres deep.

In addition, advantageously the tubular apparatus according to the invention, via the injection of fluids at high pressure within the gap between the inner wall and the outer wall of the fabric of the tubular apparatus enables:

-   -   operating in pipelines in which fluids flow at equally high         pressures without having to empty said pipelines;     -   laying of the tube without having to control the pressure inside         it; it is, in fact, sufficient to reach an overpressure in the         gap, without regulating the pressure in the internal passage,         due to swelling of the tubular apparatus;     -   temporary stiffening of the tube merely as a result of the         pressure in the gap for carrying out checks on integrity, for         temporary laying, and for inducing the tubular to follow complex         shapes of the duct that it has to reinforce or repair; and     -   injection of hardening materials (such as epoxy resins) that         have very long hardening times (since in the mean time the tube         is kept rigid and in position as a result of the overpressure in         the gap), thus opening up a wide range of operating         possibilities,

As has been mentioned above, the tubular apparatus according to the invention, unlike known tubings, which are closed at one of their ends or are closed at said end to carry out the operation of laying, advantageously comprises a sleeve, the internal passage of which, delimited by the inner wall of the three-dimensional fabric, is open at the ends, whereas just the gap enclosed between the inner wall and the outer wall of the three-dimensional fabric is closed at one end. Said aspect advantageously enables stiffening of the tubular apparatus according to the invention by controlling just the internal pressure of the gap, without having to regulate and control the pressure inside the passage in which the fluid, for example a hydrocarbon, flows, as is, instead, necessary for tubing closed at the end. This enables considerable simplification of the procedure of laying and makes it possible, before and during inflation of the tubing, to place devices for detection of the conditions of temperature, pressure, and presence of gases or liquids within the well.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what has been described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention.

The cross section of the tube is preferably constant in shape and area, but there may be envisaged at least local variations of the section, for example, to allow joints to be made.

The wall of the tube is substantially a continuous sleeve made of fabric or interwoven fibres, even though there may be considered as included in the inventive idea also walls made of fabric that include elements or short stretches made of material different from the fabric, which, however, do not modify the structure of flexible tube including at least one gap developing in an axial direction. The tubular wall preferably constitutes an entire cylindrical surface, but in the same way it may be possible for segments of arc of the perimeter to be made in a different way, and likewise the gap or gaps may not extend along the entire perimeter of the wall.

The gap or gaps preferably develop throughout the axial length of the tube, or for the stretch of axial length of the tube that has to be stiffened via injection of the fluid. Said axial length may possibly be considered but for initial or terminal stretches, for example, stretches prearranged for application of flanges, and the gap basically develops in the stretches of tube in which said tube is to become a permanent installation.

The tubular wall 11 preferably forms an entire cylindrical surface. 

1. A tubular apparatus for the continuous completion of wells for hydrocarbons, of the type comprising a flexible cylindrical wall defining inside it a hollow passage, said tubular apparatus being suitable for being wound, in particular on a spool, and laid for use in the step of completion of a drilling well, said cylindrical wall comprising a fabric defining interwoven fibres and comprising inside it at least one gap which develops in the axial direction of said cylindrical wall, said tubular apparatus being characterized in that: said fabric defines by means of the respective interwoven fibres a three-dimensional structure, comprising: an inner wall and an outer wall, which are parallel and delimit said at least one gap; and moreover means suitable for operating under traction when inside said at least one gap a pressurized fluid is present injected for stiffening the tubular apparatus, said means suitable for operating under traction comprising interconnection threads comprised in the interwoven fibres of the first, inner, wall and of the second, outer, wall that connect said first, inner, wall to said second, outer, wall through said gap.
 2. The tubular apparatus according to claim 1, characterized in that said first, inner, wall and said second, outer, wall comprise interwoven fibres of the fabric comprising warp and weft threads and said interconnection threads are weft threads or warp threads of said interwoven fibres.
 3. The tubular apparatus according to claim 1, characterized in that said cylindrical wall has a three-dimensional structure comprising a plurality of cells which develop in an axial direction of the tubular apparatus and identify said one or more gaps, walls of said cells functioning as said means suitable for operating under traction, said structure being in particular a honeycomb structure.
 4. The tubular apparatus according to claim 1, characterized in that said wall comprises an impermeabilizing material, in particular a polymeric material.
 5. The tubular apparatus according to claim 1, characterized in that said fabric of the cylindrical wall comprises aramide fibres or carbon fibres.
 6. The tubular apparatus according to claim 1, characterized in that said at least one gap is filled with said fluid injected under pressure, said fluid being in particular a resin or a cement or other material that is able to solidify.
 7. The tubular apparatus according to claim 1, characterized in that it comprises a plurality of concentric gaps, in particular two concentric gaps filled, respectively, with a resin and with its hardener and separated by a wall functionalized in such a way as to enable interchange of the fluids.
 8. The tubular apparatus according to claim 1, characterized in that said wall comprises cables for the transmission of electric power and/or laser beams and/or optical and/or electrical signals.
 9. The tubular apparatus according to claim 1, characterized in that it is comprised in a production-tubing system.
 10. The tubular apparatus according to claim 1, characterized in that it is comprised in a workover system for the repair of damaged pipes.
 11. The tubular apparatus according to claim 1, characterized in that it is comprised in a casing of a drilling well.
 12. A method for laying a flexible tubular apparatus in a step of continuous completion of wells for hydrocarbons, characterized in that lowering in said well a tubular apparatus according to claim
 1. 13. The laying method according to claim 12, said method being characterized in lowering said tubular apparatus in said well, and following upon said lowering operation injecting a fluid that is able to solidify in said at least one gap.
 14. The laying method according to claim 12, characterized in that it comprises lowering said tubular apparatus engaged to a weight.
 15. The laying method according to claim 12, characterized in that it comprises folding the free end of the tubular apparatus back outwards and securing it in the point of start of laying to obtain a folded-back portion, in particular lowering said tubular apparatus under its own weight or using drawing devices. 